1. Field of the Invention
The present invention relates to a printer having a print unit and a printing method. Particularly, the present invention relates to a printer and a printing method improved to obtain a remaining printable distance on the rear end side of paper accurately.
2. Background Art
In the related art, a printer having an inkjet print unit is provided with a paper transport mechanism for transporting paper fed thereto from a paper feed mechanism. A carriage movable in the scanning direction and a print head mounted on the carriage are provided somewhere in a paper transport path. A registration roller is provided upstream of the carriage in a transport-direction of the paper, and a registration sensor is provided upstream of the registration roller. The front end or rear end of the paper is detected on the basis of a detection signal of the registration sensor. A remaining printable distance or the like required for printing up to the vicinity of the rear end of the paper is calculated also using the transport distance of the paper transported by the transport mechanism.
The registration sensor has a rotary arm protruding to the paper transport path so as to be rotated by the paper, a photointerrupter for detecting the rotation of the rotary arm, a spring member for urging the rotary arm, and so on. It takes a predetermined operating time to for the registration sensor to turn off (changeover from presence of paper to absence of paper) after the rear end of the paper passes through the registration sensor. Thus, there occurs a detection error in paper end detection (error in transport distance) due to the operating time to. That is, the transport distance during the operating time to when the paper is transported at a low speed is short, while the transport distance during the operating time to when the paper is transported at a high speed becomes longer than that at the time of the low-speed transportation. That is, the detection error in detecting the paper end increases with the increase of the transport speed.
Therefore, an image forming apparatus according to Japanese Patent No. 3,026,917 includes a paper size detection unit for detecting the length of paper based on a detection signal from a registration sensor. The paper is transported to pass through the registration sensor at different transport speeds. A correction value corresponding to the detection error is obtained experimentally based on transport distances corresponding to the different transport speeds. The correction value obtained experimentally is applied to any image forming apparatus of the same machine type so that the paper length detected by the paper size detection unit is corrected by the correction value.
As described above, in the image forming apparatus disclosed in the aforementioned official gazette, the correction value corresponding to the detection error is obtained experimentally. The correction value obtained experimentally is applied to any image forming apparatus of the same machine type so that the paper length detected by the paper size detection unit is corrected by the correction value.
However, a registration sensor in any image forming apparatus of the same machine type has a manufacturing error proper to its constituent parts (rotary arm, spring member, etc.) individually. Thus, there is a difference in performance among registration sensors. The operating time is not also fixed.
According to the technique according to Japanese Patent No. 3,026,917, the correction value obtained experimentally is applied to any image forming apparatus of the same machine type. As a result, the detection error cannot be corrected in consideration of the difference in operating time among registration sensors. Thus, there is a limit in correcting the detection error of the paper length.
On the other hand, recent inkjet printers are very often used for printing photographs taken by digital cameras. When a photograph is printed by an inkjet printer, it may be printed on the whole surface of paper. In this case, when the detection error in detection of the rear end of the paper by a registration sensor is large, there is a problem that there occurs a blank space on the lower end side of the paper or a picture image is short thereon.